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• Characterizing the spray characteristics of casting nozzles. • Investigating the metallurgical transport under different nozzle configurations. • Morphological change process of the solidification profiles. • Revealing the formation of W-shape solidification and segregation. • Industrial trials, model validation, and prospects conducted for the dual nozzle. Solidification and segregation in a W-shape pattern are critical quality issues that have not been adequately addressed in the continuous casting of slabs. In this paper, we propose an innovative method for characterizing the spray characteristics of casting nozzles in terms of the heat transfer conditions of the width and narrow faces in the secondary cooling zone. Using a segmented numerical coupling model, we investigate the temperature transfer, solute transport, and solidification profile of liquid steel under three different nozzle configurations. Our results show that the distribution of carbon concentration in the turbulent zone is mainly influenced by the flow trajectory of the liquid steel, and that the initial positive and negative segregation caused by turbulent flow can be inherited into the final solidified slab. In the mushy zone, the distribution characteristics of carbon segregation are consistent with the solidification profiles in the natural convection zone. The solidified end zone does not solidify uniformly, and the morphology of the solidification profiles varies across different nozzle configurations. Specifically, from the eighth of the width direction of the slab to the center, the maximum temperature differences of case 1, case 2 and case 3 are 69.61, 27.60, and 63.83 K, respectively. Moreover, the carbon segregation standard deviations of case 1, case 2, and case 3 are 0.0028, 0.0013, and 0.0032, respectively. The findings suggest that the occurrence of W-shape solidification and segregation is a complex and lengthy process that depends on the metallurgical transport behavior in the secondary cooling zone, rather than the mold process parameters. Finally, we demonstrate that the proposed dual nozzle configuration (case 2) can effectively improve W-shape quality issues and enhance economic benefits, as it has been successfully implemented in the slab continuous casting caster of a state-owned steel enterprise in China. [ABSTRACT FROM AUTHOR]